These are very complex concerns.
A motion for judgement on the pleadings is done when the pleadings, even if admitted by the defendant, entitle the defendant to judgment.
A motion to dismiss is done when the plaintiff does not and can not state a cause of action based on the facts
A motion to strike seeks the court to strike out certain allegations of the complaint.
In a motion for summary judgement the defendant admits all well pled allegations but asserts that no genuine issue of materail fact exists and judgement for the defendant thereby must be granted.
Very technical stuff. Thousands of books have been written on these topics. Years of law study goes into the execution of these litigation devices.
Fine tuning Mr. Brinkmeier's response:
A motion for judgment on the pleadings is done, after the pleadings have been settled, when the pleadings, even if the allegations are admitted by the defendant, entitle the defendant to judgment because the plaintiff has failed to state facts sufficient to constitute a cause of action (in a code pleading jurisdiction) or has failed to state a claim upon which relief can be granted (in a notice pleading jurisdiction).
A motion to dismiss is filed before answering the complaint when the plaintiff does not and can not state facts sufficient to constitute a cause of action (in a code pleading jurisdiction) or has failed to state a claim upon which relief can be granted (in a notice pleading jurisdiction). In the federal courts and states which have adopted informal information exchange mandate of the federal rules of civil procedure, this may occur before the start of formal discovery.
A motion to strike asks the court to strike out certain allegations of the complaint - typically superfluous or inflammatory matter.
In a motion for summary judgment, the moving party (plaintiff or defendant) asserts that no genuine issue of material fact exists to be tried and that, on the state of undisputed facts, the moving party is entitled to judgment as a matter of law.
As Mr. Brinkmeier states, this is "very technical stuff," and trial lawyers often dispute the efficacy of motions to dismiss or strike and motions for judgment on the pleadings, since they all too often serve only to educate the plaintiff about the defects in its case. In notice pleading jurisdictions, matters have been complicated somewhat by the Supreme Court decisions in Bell Atlantic Corporation v. Twombly (2007) and the Court’s later clarification of Twombly in Ashcroft v. Iqbal (2009) . Under these decisions, to survive a motion to dismiss or a motion for judgment on the pleadings, it no longer is sufficient to merely state facts upon which a claim can be granted. Now, "for a complaint to survive a motion to dismiss, the non-conclusory ‘factual content,’ and reasonable inferences from that content, must be plausibly suggestive of a claim entitling the plaintiff to relief.” In other words, a claim must plead sufficient factual matter to enable the court to draw the reasonable inference that the defendant is liable for the misconduct alleged; otherwise, the claims have no facial plausibility and do not state a claim against that defendant. These decisions have raised the bar in notice pleading jurisdictions and should weed out implausible claims, reducing the burden they impose on the courts.
Disclaimer: This answer is provided as a courtesy. This response does not constitute legal advice, which requires an attorney-client relationship, and this response does not create an attorney-client relationship between us. It is impossible to properly evaluate a legal problem without a detailed consultation and a comprehensive review of all the facts, documents, and/or other materials involved. In addition, if you are in a state other than California (where I am admitted to practice), your state may have different laws. You therefore should not rely on this answer, but should consult with local counsel for definitive guidance.
Alan Brinkmeier has given an excellent discussion of the procedural area. In Missouri "demurrer" is not longer used so is not relevant. In either case, you should be using an attorney
This comment does not create an attorney-client relationship. The law and its application by the courts is constantly evolving and changing. This discussion is not to be taken as a definitive guide, and should not be relied upon to determine all fact situations. Each set of facts must be examined separately with the current case and statutory law analyzed and applied accordingly.